Surface-seismic waveform data are used to generate images of the sub-surface geological structures. In principle, the acoustic impedance at a specific location is calculated as the ratio between the in-coming and the reflected energy. Vertical Seismic Profiling is a technique whereby reflection from the subsurface is recorded on down-hole geophones or receivers from wave fields generated by a surface seismic source.
Some processing methods use a parametric least-square method to decompose the wavefield incident on the receiver array locally into four plane waves: up- and down-going compressional, and up- and down-going shear polarized in the vertically plane (see Leaney, W. S. and C. Esmersoy, 1989, Parametric Inversion of offset VSP wavefields: 59th Annual International Meeting, SEG, Expanded Abstracts, 26-29). In more simplistic processing of VSP data, the incident wavefield is separated into down-going and up-going wavefield components. The up-going components of the wavefield are next deconvolved with the down-going components (see, e.g., Haldorsen, J. B. U., Miller, D. E., and Walsh, J., 1994, Multichannel Wiener deconvolution of vertical seismic profiles, Geophysics, 59, 1500-1511).
The deconvolved compressional or shear waves can be used to create images of the formation below the well using migration algorithms designed for this purpose (e.g., Miller, D., Oristaglio, M., and Beylkin, G., 1987, A new slant on seismic imaging: Migration and integral geometry: Geophysics, 52, 943-964, as applied by Haldorsen, J. B. U., 2002, Converted-shear and compressional images using Projection Imaging, paper F031, 64th Annual Meeting and Exhibition, European Association of Geoscientist and Engineers).
Bostock, et al., (see Bostock, M. G., S. Rondenay, and J. Shragge, Multiparameter two-dimensional inversion of scattered teleseismic body waves, 1, Theory for oblique incidence, J. Geophys. Res., 106, 30,771-30,782, 2001) and Shragge et al. (see Shragge, J., M. G. Bostock, and S. Rondenay, Multiparameter two-dimensional inversion of scattered teleseismic body waves, 2, Numerical examples, J. Geophys. Res., 106, 30,783-30,794, 2001), have developed a method whereby they decompose the p-wave coda from teleseismic events (seismic signals generated by distant earthquakes) into compressional and shear waves components, incident on a surface array of receivers. Rondenay et al., (see Rondenay, S., M. G. Bostock, and J. Shragge, Multiparameter two-dimensional inversion of scattered teleseismic body waves, 3, Application to the Cascadia 1993 data set, J. Geophys. Res., 106, 30,795-30,808, 2001) have applied this to generate an image of the moho—the boundary between the earth crust and mantle—located about 40 km below a surface array of receivers. Essentially the method applied by Rondenay, et al., is similar to the method that is used for finding the locations of epicenters in earthquake and in passive seismic monitoring (e.g. Michaud, G., Leslie, D., Drew, J., Endo, T., and Tezuka, K., 2004, “Microseismic event localization and characterization in a limited aperture HFM experiment”, 74th Annual International Meeting, SEG, Expanded Abstracts, pp. 552-555).